Digestion & Absorption Of Lipids Flashcards
What are the most common classes of lipids?
Triacylgylcerols/triglycerides
- 3 fatty acids bound to a glycerol backbone
Glycerophospholipid
- phospholipid that has a glycerol background
Sphingolipids
Steroids
Fatty acids
- unsaturated = has double bonds
- saturated = doesnt have double bonds
What fatty acids are essential?
Linoleic acid (18,2) - originates from omega-6
linolenic acid (18,3)
- originates from omega-3
- makes EPA and DHA byproducts
*are essential because they make arachidonic acid which are precursors for PGEs and leukotrienes
humans cannot synthesis fatty acids that contain cis-double bonds beyond position 9
What is arachidonic acid a precursor for?
Prostaglandins
Leukotrienes
Triacylglycerol functions
Primary storage form of energy and is the major macronutrient for lipids
Can be saturated or unsaturated/trans fats
Metabolic effects of each type of dietary fat
1) trans FA’s
- increases LDL and decreases HDL
- high levels increase CAD
2) saturated FA’s
- increases LDL with no effect on HDL
3) monounsaturated FA’s
- decreases LDL and slightly increases HDL
- decreases incidence of CAD
4) polyunsaturated omega-3 (linoleic acid)
- decreases LDL and HDL
- * produces arachidonic acid
- decreases risk of CAD
5) polyunsaturated omega-6 (DHA/EPA)
- no effect on LDL and HDL
- *most healthy one
- decreases incidence of CAD and SUD
What diseases are tied to high levels of lipids?
Heart disease
Malignant cancer
Stroke/ clotting issues
Diabetes
does dietary levels of cholesterol and fatty acids have a strong influence on plasma concentrations of each?
NO
What is the daily level of cholesterol produced by the liver?
1000mg
Classes of lipoproteins with associated apolipoproteins
1) HDL
- A-1/2 and E apolipoproteins
- ONLY has cholesteryl esters
2) LDL
- B100 apolipoproteins
- ONLY has cholesteryl esters
3) VLDL
- B100, E and C apoplipoproteins
- has more Triglycerides than cholesteryl esters
4) Chylomicrons
- A-1/4/5 and B48 apolipoproteins
- has wayyy more triglycerides than cholesteryl esters
What are phytosterols?
Mimic human cholesterol and signal the body to make less cholesterol
- also the body absorbs less cholesterol and empties it out
Emulsification
Process that occurs in the small intestine and requires bile
- prevents fat aggregation of cholesterol and triglycerides so that pancreatic lipase can do its job and break it down properly before it reaches the large intestine
Bile + TAGS/cholesterol = emulsion droplets
- emulsion droplets increase surface are for pancreatic lipase to function
What two complementary actions are done in emulsification?
Mechanical agitation
Secretion of bile salts
promote the production of increasingly smaller particles which increases the accessibility of lipids by pancreatic lipase in the small intestine
What is bile salts primary function?
Other than emulsification, stabilize small particles to prevent them from coalescing
What is the general overview of triacyglycerol digestion
1) TAGs enter body and the stomach
2) gallbladder releases bile salts and pancreas releases bicarbonate/pancreatic/coliapse lipase
3) combining from #2, TAGs -> emulsification droplets (single TAGs instead of multiple TAGs)
4) single TAGs are degraded by pancreatic lipase into Fatty acids + 2-monoacylglycerol (2-MG)
5) FAs + 2-MG -> micelles and nascent chylomicrons
6) nascent chylomicrons go back into blood stream via lymph and Bile salts/ collapse lipase go into ileum
What hormone causes the release of bicarbonate ions?
Secretin
- releases in response to the low pH of chime
- combats the low pH and provides appropriate pH for optimal pancreatic enzyme functions
Also CCK
What is the function of pancreatic lipase and colipase specifically?
both are released from the pancreas
Pancreatic:
- esterase that cleaves FAs that are emulsified at carbon 1 and 3.
- produces 2-MG and an FA from each TAG
Colipase:
- binds/anchors pancreatic lipase to promote enzymatic activity of pancreatic lipase
Phospholipid digestion
Undergoes multiple rounds of digestion from 2 enzymes
1) phospholipase A2
- removes FAs from position 2 in a phospholipid
- produces lysophospholipid and a free FA
2) lysophospholipase
- removes FAs from position 1 from lysophospholipase
- produces glycerylphosphoryl base and a free FA
glyceralphosphoryl base gets recycled again through this mechanism or excreted via feeces
What is the role of cholecystokinin (CCK)
Is a small peptide hormone that is released from mucosa cells of duodenum and jejunum
- is released only in response to presence of lipids and partially digested proteins
CCK = causes contraction of gallbladder and stimulation of exocrine cells of the pancreas. Also causes decreases in gastric motility
- causes release of bile and pancreatic enzymes
What cells are lipids absorbed into the body by?
Enterocytes
What is the fate of chylomicrons within the body after being produced in the small intestine?
1) renter the bloodstream via lymphatics
2) releases FA’s to muscles and adipose tissues
3) enters the liver and is uptaken by the liver, degreased by liver lysosomes
4) produces FA’s, cholesterol, AAs and glycerol byproducts
What is the role of microsomes trigylceride transfer protein (MTP)?
Transfers lipids to apoB-48 as it is produced
Transfers lipid from cytoplasm to the ER lumen
ultimately blinds to apoB-48 particles and marks it for golgi secretion
Abetalipoproteinemia
Bassein-Kornzweig syndrome
Defects in the MTP proteins
- results in a complete absence of Apo-B containing lipoproteins
Affects absorption of dietary fats/cholesterol and fat-soluble vitamins (DEAK)
Symptoms:
- failure to thrive
- diarrhea
- star-shaped red blood cells
- fatty stools
- blindness/difficultly seeing
What affects can sickle cell disease have on the GI tract?
Cholecystits
How does orlistat cause weight loss?
Inhibits activity of pancreatic lipase
- reduces fat digestion and absorption
Works by forming a covalent bond with serine residues on gastric and pancreatic lipase
